The present invention pertains to light modification by birefringent materials, waveguides, interferometry and spectrometry and more particularly pertains to waveguide liquid crystal optical devices.
U.S. Pat. Nos. 4,928,007 and 4,969,742 teach integrated optical chips which have interferometers having optical waveguides and a birefringent crystal of a material such as lithium niobate. The optical path length through the crystal is varied by imposing a electrical field across the crystal. The crystals in these devices present a major shortcoming in that the crystals have small electrooptic coefficients and thus require the imposition of large voltages and produce very small changes in optical path.
Liquid crystals have been utilized in optical waveguide devices to provide a variety of results. Optical modulators are described by Okamura, Y. et. al. in "Low-Voltage Driving in Nematic Liquid Crystal Overlayered Waveguide", Journal of Lightwave Technology, Vol. LT-4, No. 3, (March 1986), pp 360-363; Okamura, Y. et. al. in "Electrooptic Leaky Anisotropic Waveguides Using Nematic Liquid Crystal Overlayers", Journal of Lightwave Technology, Vol. LT-2, No. 3, (June 1984) pp 292-295; and Green M. et. al. in "Flat-Panel Liquid-Crystal Waveguide Display", Proceedings of the Society for Information Display, Vol. 26, No. 2, (1985) pp 163-165. These papers teach devices which use a liquid crystal cell to selectively make a waveguide "leaky". The indexes of a waveguide and liquid crystal material on or near the waveguide are selected such that a potential, applied by adjoining electrodes, causes propagated light to be coupled out of the waveguide.
Optical switches described by Terui, H. et. al. in "8.times.8 Optical Waveguide Switch Using Liquid Crystal", SPIE, Vol. 517-Integrated Optical Circuit Engineering, (1984), pp 267-274 and Verly, P.G., "Low Loss Liquid-Crystal-Clad Waveguide Switch with a Large Angular Separation of the Optical Beam", Canadian Journal of Physics, Vol. 65, (1987), pp 476-483 are not "leaky", however, the exit site of a propagated beam is switched by using liquid crystal material to cause reflection or transmittance of light at a boundary. A waveguide beam deflector, described by Hu, C. et. al. in "Optical Deflection in Thin-Film Nematic-Liquid-Crystal Waveguides", IEEE Journal of Quantum Electronics, Vol. QE-10, No. 2, (February 1974), pp 218-222, scatters propagated light in a thin film waveguide into multiple modes and uses an imposed voltage to variably couple the light out of the waveguide. It has been shown by C. Hu and J. R. Whinnery in "Field-Realigned Nematic Liquid Crystal Optical Waveguides", IEEE Journal of Quantum Electronics, Vol. QE-10, No. 7, July 1974, PP. 556-562, that optical waveguides formed with LC layers in which the director rotates in the plane defined by their guided mode propagation vector and the normal to the plane of the guide member exhibit stationary transverse electric (TE) and transverse magnetic (TM) eigenmodes. The TE eigenmodes are characterized by electric field vectors lying in the plane of the guide member and by effective indexes of refraction which are independent of the applied voltage. TM eigenmodes are characterized by magnetic field vectors lying in the plane of the guide member and effective indexes of refraction which depend upon the applied voltage.
U.S. Pat. Nos. 4,779,959 to Saunders, 4,595,292 to Amodeo et. al., and 4,909,626 to Purvis et. al. each teach optical devices in which an electrical field imposed on a liquid crystal cell changes an optical path length. Each of these patents have the shortcoming that the liquid crystal dimension is very small and a delay induced is limited to a few waves. (Wave retardation or delay is equal to the optical path difference divided by the wavelength.)
U.S. Pat. No. 4,725,141 to Georgiou et. al. teaches a Mach Zehnder interferometer in which beam splitters and mirrors are replaced by continuous optical fibers. The optical path length of one arm is changed by heating or surrounding the optical fiber with liquid crystal to change the effective index of refraction. The use of electrodes is not disclosed.